Semiconductor device with resistance circuit

ABSTRACT

Provided is a resistance circuit having a resistance element with high resistance and high accuracy. An insulating film such as a silicon nitride film is formed on the resistance element made of a thin film material whose thickness is reduced to 500 Å or smaller. The insulating film prevents passing through of the contact hole arranged on the resistance element during etching for forming the contact hole.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having asemiconductor integrated circuit with a resistance circuit formed on thesame semiconductor substrate.

2. Description of the Related Art

In a semiconductor integrated circuit following types of resistors areused; a diffused resistor made from a monocrystalline siliconsemiconductor substrate into which impurities of a conductivity typeopposite to that of the semiconductor substrate are introduced, and apolycrystalline silicon resistor made of polycrystalline silicon intowhich impurities are introduced.

A sectional view in which a resistance element used for a conventionalresistance circuit and an insulated gate field effect transistor(hereinafter, abbreviated to MISFET) are combined is shown in FIG. 2.

A MISFET 102 includes a thin gate oxide film 3, source and drain regions4, and a gate electrode 5. The MISFET 102 is surrounded by a thickisolation oxide film 2. On those films, an intermediate insulating film8 is formed, and electrical connection is achieved by metal wiring 10via contact holes 9.

Further, a resistance element 101 is formed of a polycrystalline siliconfilm deposited on the flat and thick isolation oxide film 2.

In the polycrystalline silicon film forming the resistance element,there are formed high concentration impurity regions 6 at both ends ofthe polycrystalline silicon film and a low concentration impurity region7 sandwiched between the high concentration impurity regions 6. Theresistance value of the resistance element is determined depending on aresistivity, which is determined depending on the impurity concentrationof the low concentration impurity region 7 having high resistance, andthe length and the width of the low concentration impurity region 7. Thehigh concentration impurity regions 6 are used for obtaining ohmiccontact with respect to the metal wiring.

The intermediate insulating film 8 is formed on the resistance element101, and electrical connection is achieved by the metal wiring 10 viathe contact holes 9. In the resistance circuit used for thesemiconductor integrated circuit, a plurality of the resistance elementsof FIG. 2 are formed on the same substrate surface so as to be connectedin series or in parallel to one another via the metal wiring.

The intermediate insulating film 8 formed on the MISFET 102 and theresistance element 101 contains boron or phosphorus, and is flattenedthrough thermal treatment of 850° C. or higher. Thus, the difference inheight in the semiconductor integrated circuit caused by the filmpatterns is reduced. Further, after the metal wiring is formed, asilicon nitride passivation film 11 is provided thereon as a protectivefilm.

The contact holes provided in the flattened intermediate insulating film8 as described above have depths that differ depending on the underlyingstructures. In the example described above, since parts of theintermediate insulating film provided on the source and the drain in thesemiconductor substrate are the thickest, and a part of the intermediateinsulating film provided on the resistance element is the thinnest, thecontact holes for the source and the drain are the deepest, and thecontact holes for the resistance element are the shallowest when thecontact holes are formed in the respective parts.

When the contact holes with two depths are formed simultaneously, thecontact holes for the resistance element, on which the thin intermediateinsulating film is provided, are finished first, and hence until thecontact holes for the source and the drain are completely made,excessive over-etching is performed on the contact holes for theresistance element. Accordingly it is necessary to set the thickness ofthe polycrystalline silicon film to be thick enough to prevent thecontact hole from passing through the resistance element during theover-etching, or it is necessary to ensure the resistance to etching.

As a method for solving the above-mentioned problem, for example, suchmethods illustrated in FIGS. 3 and 4 are proposed.

In FIG. 3, in order to improve the strength to the over-etching, thecontact hole 9 for connection with the metal wiring 10 is formed onthick polycrystalline silicon film 15. Meanwhile, the resistance elementmain body 7 is formed of a thin polycrystalline silicon film, and thethick polycrystalline silicon film and the thin polycrystalline siliconfilm are connected to each other through via holes 13 providedseparately from the contact hole 9 for connection with the metal wiring10.

Further, in FIG. 4, the corresponding part to the thick polycrystallinesilicon film in FIG. 3 is replaced by an impurity diffusion region 17formed in the semiconductor substrate. Then, similar to the case of FIG.3, the resistance element main body is formed of a thin polycrystallinesilicon film, and the impurity diffusion regions and the thinpolycrystalline silicon are connected to each other through via holes 13provided separately from the contact holes 9 for connection with themetal wiring.

Such method of providing a polycrystalline silicon resistor is disclosedin, for example, Japanese Published Patent Application H09-051072.

As for manufacturing the conventional resistance element, the followingproblems arise.

For example, when the polycrystalline silicon resistor is employed, inorder to aim for improvement in accuracy of the resistance value orincrease in resistance value, the reduction of the thickness of thepolycrystalline silicon film is aimed for in some cases. Particularly inrecent years, along with advancement of devices and improvement incontrollability of the thickness of the film to be deposited, it hasbecome easier to realize a thin film. However, as described above, thinfilms have a problem of resistance to over-etching, and hence it hasbeen difficult to utilize a resistance element formed of a thin film of500 Å or smaller in the semiconductor integrated circuit.

In order to realize a resistance element formed of a thin film with amethod other than those illustrated in FIGS. 3 and 4, there is a methodof forming the resistance element by performing photomasking steps andetching steps separately for respective contacts. However, this methodhas a problem of causing increase in cost due to addition of the maskingstep. Further, when the contact holes having one depth are formed afterthe contact holes having another depth are formed, it is necessary toperform the photolithography process while the contact holes formedearlier are opened, which may cause contamination and adhesion offoreign matters and reduce the quality.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems, the present inventionemploys the following measures.

That is, a semiconductor device includes a resistance circuit including:

-   -   a resistance element formed of a first thin film;    -   a second thin film formed on the resistance element;    -   an intermediate insulating film formed on the second thin film;    -   a contact hole for the resistance element, the contact hole        passing through the second thin film and being provided in the        intermediate insulating film at a depth reaching the first thin        film; and    -   a metal wiring formed on the contact hole.

Alternatively, in the semiconductor device including the resistancecircuit, the second thin film is formed on the first thin film and hasthe same shape in plan view as the resistance element formed of thefirst thin film.

Alternatively, in the semiconductor device including the resistancecircuit, the second thin film is formed on the first thin film and isformed in separated regions each including the contact hole.

Alternatively, in the semiconductor device including the resistancecircuit, the second thin film is formed on the first thin film and isformed in a region including the resistance element formed of the firstthin film, the region being wider than the resistance element.

Further, in the semiconductor device including the resistance circuit,the first thin film has a thickness of 500 Å or smaller.

Further, in the semiconductor device including the resistance circuit:the first thin film is a first polycrystalline silicon film; and thefirst polycrystalline silicon film contains impurities of a firstconductivity type at an impurity concentration in a range of 1×10¹⁵atoms/cm³ to 5×10⁹ atoms/cm³.

Alternatively, in the semiconductor device including the resistancecircuit, the first thin film is a thin film made of one of CrSi, CrSiN,CrSiO, NiCr, and TiN.

Alternatively, in the semiconductor device including the resistancecircuit, the second thin film is a second polycrystalline silicon filmcontaining impurities of a second conductivity type, which is oppositeto the first conductivity type of the first polycrystalline siliconfilm.

Alternatively, in the semiconductor device including the resistancecircuit, the second thin film is a second polycrystalline silicon filmwhich does not contain impurities.

Alternatively, in the semiconductor device including the resistancecircuit, the second thin film is a silicon nitride film.

Further, in the semiconductor device including the resistance circuit,the second thin film has a thickness in a range of 150 Å to 350 Å.

According to the present invention, it is possible to provide asemiconductor device formed of a semiconductor integrated circuit havinga built-in resistance element with high accuracy and high resistancesine it becomes easier to form a thin film of 500 Å or smaller for theresistance element.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic sectional view illustrating a resistance elementand a MISFET according to a first embodiment of the present invention;

FIG. 2 is a schematic sectional view illustrating a conventionalresistance element and a conventional MISFET;

FIG. 3 is a schematic sectional view of a conventional resistanceelement;

FIG. 4 is a schematic sectional view of a conventional resistanceelement;

FIGS. 5A to 5C are sectional views illustrating a process flow formanufacturing the resistance element and the MISFET according to thefirst embodiment of the present invention;

FIGS. 6A to 6C are sectional views illustrating the process flow formanufacturing the resistance element and the MISFET according to thefirst embodiment of the present invention, which follows the processflow illustrated in FIGS. 5A to 5C;

FIG. 7 is a schematic sectional view illustrating a resistance elementand a MISFET according to a second embodiment of the present invention;

FIG. 8 is a schematic sectional view illustrating a resistance elementand a MISFET according to a third embodiment of the present invention;and

FIG. 9 is a schematic sectional view illustrating a resistance elementand a MISFET according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention are described withreference to the drawings.

FIG. 1 is a schematic sectional view of a semiconductor integratedcircuit having a built-in resistance element according to a firstembodiment of the present invention. A resistance element 101 of thepresent invention for a resistance circuit and a MISFET 102 which is aninsulated gate field effect transistor are combined.

Similar to the conventional case, the MISFET 102 includes a thin gateoxide film 3, source and drain regions 4, and a gate electrode 5. TheMISFET 102 is surrounded by a thick isolation oxide film 2. On thosefilms, an intermediate insulating film 8 is formed, and electricalconnection is achieved by metal wiring 10 via contact holes 9.

Meanwhile, the resistance element 101 is formed of a polycrystallinesilicon film deposited on the flat and thick isolation oxide film 2 on asemiconductor substrate 1, and further, an insulator such as a siliconnitride film 12 is deposited thereon.

Similar to the conventional case, in the polycrystalline silicon formingthe resistance element, a low concentration impurity region 7 and highconcentration impurity regions 6 at both ends of the low concentrationimpurity region 7 are formed. The resistance value of the resistanceelement is determined depending on the impurity concentration of the lowconcentration impurity region 7 having high resistance, and the size ofthe low concentration impurity region 7. The high concentration impurityregions 6 are used for obtaining ohmic contact with respect to the metalwiring 10. The silicon nitride film 12 formed thereon is an insulatingfilm, and hence the resistance value of the resistance element isbasically determined depending on the impurity concentration of the lowconcentration impurity region.

The intermediate insulating film 8 is formed on the resistance element101, and electrical connection is achieved by the metal wiring 10 viathe contact holes 9. At this time, those contact holes 9 pass throughboth the intermediate insulating film 8 and the silicon nitride film 12formed on the resistance element, to thereby reach the highconcentration impurity regions 6 of the polycrystalline silicon formingthe resistance element. Thus, electrical connection is obtained.

The depths of the contact holes provided in the intermediate insulatingfilm 8, which is flattened through, for example, thermal treatment,differ depending on the underlying structures, and the contact holes forthe resistance element are the shallowest. Accordingly, when all of thecontact holes are formed in the same masking step, in the conventionalcase, the contact holes for the resistance element, on which the thinintermediate insulating film is provided, are finished first and henceuntil all of the contact holes are completely made, excessiveover-etching is performed on the contact holes for the resistanceelement. Consequently, the contact holes pass through the resistanceelement in some cases when the resistance element is thin.

However, the silicon nitride film provided additionally on theresistance element in the present invention has a low etching ratecompared to that of the intermediate insulating film, and hence there isan effect to delay the time that the contact holes pass through theresistance element. Accordingly, even when a thin polycrystallinesilicon of 500 Å or smaller is used as the resistance element, thepassing through of the contact hole does not occur, and hence it ispossible to obtain a good contact.

Referring to FIGS. 5A to 6C, an example of a method of manufacturing thesemiconductor integrated circuit according to the present invention isdescribed.

First, as illustrated in FIG. 5A, the semiconductor substrate 1 isprepared, and by conventionally existing technologies such as a LOCOSoxide film forming step, a gate oxide film forming step, a gateelectrode forming step, and a source and drain region forming step,there are formed the thick oxide film 2, the gate oxide film 3, the gateelectrode 5, and the source and drain regions 4, which are main portionsof the MISFET.

Next, as illustrated in FIG. 5B, a polycrystalline silicon thin filmforming the resistance element is deposited after an interlayerinsulating film 15 is deposited on the entire surface. The interlayerinsulating film is used for separating the polycrystalline siliconforming the gate electrode of the MISFET and the polycrystalline siliconforming the resistance element. The polycrystalline silicon thin filmforming the resistance element is formed to have a thickness of 500 Å orsmaller so as to achieve high resistance or high accuracy.

Next, impurity implantation for setting the resistivity is performed inthe entire polycrystalline silicon film on the semiconductor substrate,to thereby farm the polycrystalline silicon low concentration impurityregion 7. The resistivity of the resistance element is adjusted by anamount of this impurity implantation. The impurities to be used arephosphorus or arsenic, which is an N-type impurity, or boron or BF₂,which is a P-type impurity, and the impurity implantation amount thereofis set, although depending on the desired resistivity, within a range of1×10¹⁵ atoms/cm³ to 5×10¹⁹ atoms/cm³.

Next, the silicon nitride film 12, which is specific to the presentinvention, is deposited on the entire semiconductor substrate by anarbitrary method such as LPCVD and sputtering.

Next, as illustrated in FIG. 5C, through a photomasking step and anetching step, the deposited polycrystalline silicon film and siliconnitride film 12 are processed to the shape of the resistance element. Atthis time, both of the polycrystalline silicon film and the siliconnitride film are etched with use of the same resist, and thephotomasking step is not added. Though the step of depositing thesilicon nitride film, which is specific to the present invention, isadded, there is minimal cost increase. Then, through anotherphotomasking step, the high concentration impurity regions 6 are formedin the polycrystalline silicon.

The high concentration impurity implantation step can be carried out asa high concentration impurity implantation step for forming the sourceand the drain of the MISFET. That is, when the resistance element is anN-type resistance element, N-type source and drain impurities maybe usedas the high concentration impurities, and when the resistance element isa P-type resistance element, P-type source and drain impurities may beused as the high concentration impurities. In so doing it is possible tofurther reduce a photomasking step and obtain a cost reduction effect.

Next, as illustrated in FIG. 6A, the intermediate insulating film 8 isformed on the semiconductor substrate. The formation method therefor isas follows. After an oxide film containing phosphorus or boron isdeposited, the deposited insulating film is flattened by, for example, areflow method in which flattening is performed through thermal treatmentof 850° C. or higher, or by an etch-back method or by a CMP method.

Next, as illustrated in FIG. 6B, through a photomasking step, thecontact holes 9 are formed all at once by dry etching at necessaryportions of the intermediate insulating film corresponding to, forexample, the source and drain regions, the gate electrode, and theresistance element. At this time, the contact holes 9 for the resistanceelement pass through the silicon nitride film on the polycrystallinesilicon film to reach the polycrystalline silicon film. However, thesilicon nitride film has an appropriate thickness, and hence even whenthe polycrystalline silicon film is thin, passing through of the contacthole does not occur.

Next, as illustrated in FIG. 6C, deposition of a metal film, patternformation of the metal wiring 10, and deposition and pattern formationof a passivation film 11, which is the final protective film, areperformed. With this, the semiconductor integrated circuit including theresistance element according to this embodiment is completed.

Among the steps, in the contact hole forming step illustrated in FIG.6B, depending on the shape and structure under the intermediateinsulating film, the depths of the contact holes partially differ fromone another. For example, the deepest portion is the contact hole forthe source and drain regions, and the shallowest portion is the contacthole for the resistance element. The difference therebetween may expandfrom 3,000 Å to 7,000 Å in some cases. In the conventional manufacturingmethod, after the contact holes for the resistance element are opened,excessive over-etching is performed in the contact holes for theresistance element by an amount corresponding to at least 3,000 Å to7,000 Å of the intermediate insulating film until other contact holesare completely opened. Accordingly, when the polycrystalline siliconfilm of 500 Å or smaller is used as the resistance element, it has beendifficult to prevent the passing through of the contact hole.

In the present invention, the thickness of the silicon nitride film onthe polycrystalline silicon film described above is appropriatelyadjusted, and hence the above-mentioned passing through can beprevented. The film thickness is inevitably determined depending on, forexample, the film thickness difference of the intermediate insulatingfilm described above, the etching condition, and the quality of thesilicon nitride film.

For example, when the selection ratio of the intermediate insulatingfilm and the silicon nitride film during the contact etching is 20:1,and when the intermediate insulating film thickness difference betweenat the resistance element and at the source and drain regions is 5,000Å, the thickness of the silicon nitride film provided on thepolycrystalline silicon forming the resistance element may be set to 250Å, which is 1/20 of 5,000 Å corresponding to the intermediate insulatingfilm thickness difference. Generally, considering a case where theintermediate insulating film thickness difference in the above-mentionedrange is generated, it is reasonable to select the silicon nitride filmthickness from the range of 150 Å to 350 Å. In this manner, it ispossible to stably manufacture a resistance element formed ofpolycrystalline silicon of 500 Å or smaller, which has been difficult torealize in a conventional case.

By the way, when the thickness of the polycrystalline silicon film to beused for the resistance element is reduced, it is possible to realizehigh resistance and high accuracy of the resistance value. The reasonsare as follows.

It is needless to say that, when the impurity concentration in thepolycrystalline silicon film forming the resistance element is the same,as the polycrystalline silicon film becomes thinner, the sectional areaof the resistor decreases, and hence the resistance increases.

Meanwhile, when the resistance value is the same, as the polycrystallinesilicon film becomes thinner, the impurity concentration is set higher,and hence the resistance value fluctuation reduces, which realizes highaccuracy. This is because most part of the resistance value formed bythe polycrystalline silicon depends on carriers to be captured at in theinterface state existing between the grains of the polycrystallinesilicon, and hence the rate that the carrier concentration fluctuationaffects the resistance value fluctuation is high. The carrierconcentration fluctuation is determined depending on the implantationimpurity concentration, and when the impurity concentration is high, thefluctuation is alleviated. Accordingly, the reduction in thickness ofthe polycrystalline silicon film is effective for improving accuracy ofthe resistance value of the resistance element.

FIG. 7 is a schematic sectional view of a semiconductor integratedcircuit having a built-in resistance element according to a secondembodiment of the present invention. In this example, the siliconnitride film 12 is formed on the high concentration impurity regions 6of the resistance element, but the silicon nitride film is not formed onthe low concentration impurity region 7 of the resistance element. Inorder to realize this structure, the pattern formation of the resistanceelement and the pattern formation of the silicon nitride film 12 areseparately performed, and compared to the structure of FIG. 1, it isnecessary to add one photomasking step. Since the patterning accuracy ofthe silicon nitride film, however, does not affect the pattern formationof the resistance element, and hence it is possible to improve theaccuracy of the resistor width at the time of etching of the resistanceelement, and is possible to obtain a resistance element having ahigh-accuracy resistance value. Further, there is an effect of reducinga parasitic capacitance between the resistance element and the uppermetal wiring.

FIG. 8 is a schematic sectional view of a semiconductor integratedcircuit having a built-in resistance element according to a thirdembodiment of the present invention. In this example, the siliconnitride film 12 to be formed on the resistance element is formed wide soas to sufficiently overlap the resistance element. Similar to the secondembodiment, the pattern formation of the resistance element and thepattern formation of the silicon nitride film are separately performed.In this manner, similar to the second embodiment, the pattern formationof the resistance element can be performed without being affected by thepatterning accuracy of the silicon nitride film, and hence it ispossible to improve the accuracy of the resistor width at the time ofetching of the resistance element, and is possible to obtain aresistance element having a high-accuracy resistance value.

FIG. 9 is a schematic sectional view of a semiconductor integratedcircuit having a built-in resistance element according to a fourthembodiment of the present invention. In this example, the film formed onthe resistance element, which is the silicon nitride film in FIG. 1, isreplaced by a polycrystalline silicon film 14 which does not containimpurities. Impurities are not implanted into this polycrystallinesilicon film, and hence the polycrystalline silicon film has very highresistivity. Even when the polycrystalline silicon film is laminated,the resistance value of the underlying resistance element does not vary.Further, at the time of pattern formation of the resistance element, thepolycrystalline silicon film of the resistance element and the anotherpolycrystalline silicon film provided thereon can be etched at the sametime under the same etching condition, and hence compared to the case ofthe first embodiment, the number of steps of the etching processing canbe reduced. Thus, it is possible to obtain a resistance elementeffective for cost reduction owing to the reduction in the number ofsteps, the resistance element having a high-accuracy resistance valueand being high in process accuracy of the resistor width.

Further, as a fifth embodiment, the film formed on the resistanceelement, which is the polycrystalline silicon film which does notcontain impurities in the fourth embodiment, can be replaced by apolycrystalline silicon film containing impurities of a conductivitytype opposite to that of the resistance element. Since thepolycrystalline silicon film forming the resistance element and anotherpolycrystalline silicon film covering the polycrystalline silicon filmforming the resistance element contain impurities of conductivity typesopposite to each other, an electric insulating property is maintained,and the resistance value of the underlying resistance element does notvary due to the covering of the another polycrystalline silicon filmprovided on the resistance element.

Still further, the film to be formed on the resistance element is notlimited to the silicon nitride film or the polycrystalline silicon filmas long as the etching selection ratio with respect to the intermediateinsulating film is high and the insulating property with respect to theunderlying resistance element is sufficiently maintained. That is,various metal oxides, metal nitrides, and carbon compounds may beselected as the film to be formed on the resistance element.

Further, the film forming the resistance element of the presentinvention is not limited to the polycrystalline silicon film. It isneedless to say that this film is also applicable to a resistor thinfilm such as a metal thin film made of, for example, CrSi, CrSiN, CrSiO,NiCr, or TiN having a very small thickness of about 500 Å or smaller,through which a contact hole may otherwise pass at the time of theetching processing when the resistor thin film is simply replaced by apolycrystalline silicon film.

1. A semiconductor device, comprising: a resistance circuit; and aninsulated gate field effect transistor, the resistance circuitcomprising: a resistance element formed of a first thin film arranged onan isolation oxide film provided on a surface of a semiconductorsubstrate; a second thin film formed on the resistance element; anintermediate insulating film formed on the second thin film; a contacthole for the resistance element, the contact hole passing through thesecond thin film and being provided in the intermediate insulating filmat a depth reaching the first thin film; and a metal wiring formed onthe contact hole; wherein the insulated gate field effect transistor isprovided in a region of the semiconductor substrate surrounded by theisolation oxide film.
 2. A semiconductor device according to claim 1,wherein the second thin film is formed on the first thin film and hasthe same shape in plan view as the resistance element formed of thefirst thin film.
 3. A semiconductor device according to claim 1, whereinthe second thin film is formed on the first thin film and is formed inseparated regions each including the contact hole.
 4. A semiconductordevice according to claim 1, wherein the second thin film is formed onthe first thin film and is formed in a region including the resistanceelement formed of the first thin film, the region being wider than theresistance element.
 5. A semiconductor device according to claims 1,wherein the first thin film has a thickness of 500 Å or smaller.
 6. Asemiconductor device according to claims 1, wherein: the first thin filmcomprises a first polycrystalline silicon film; and the firstpolycrystalline silicon film contains impurities of a first conductivitytype at an impurity concentration in a range of 1×10¹⁵ atoms/cm³ to5×10¹⁹ atoms/cm³.
 7. A semiconductor device according to claims 1,wherein the first thin film comprises a thin film made of one of CrSi,CrSiN, CrSiO, NiCr, and TiN.
 8. A semiconductor device according toclaims 1, wherein the second thin film comprises a silicon nitride film.9. A semiconductor device according to claim 6, wherein the second thinfilm comprises a second polycrystalline silicon film containingimpurities of a second conductivity type, which is opposite to the firstconductivity type of the first polycrystalline silicon film.
 10. Asemiconductor device according to claim 6, wherein the second thin filmcomprises a second polycrystalline silicon film which does not containimpurities.
 11. A semiconductor device according to claim 8, wherein thesecond thin film has a thickness in a range of 150 Å to 350 Å.